UnitValidator provides a rails model validator using ruby-units to detect valid units of measurement
Just add this to your Gemfile:
gem 'unit_validation'
and run
bundle install
Put something like this in your models:
validates :height, :unit => true
validates :count, :unit => {:allowed_types => :unitless}
validates :width, :unit => {:allowed_types => [:mass, :length]}
The error message upon failure can be overridden by passing the option message to the unit validation:
validates :quantity, :unit => {:message => 'please be so kind as to enter a physical quantity'}
If not supplied, a localised message is shown. Translations are kept in localeapp#6170 - please feel free to add a new translation or correct something.